4. Give the factors of a2 - 81.
A. (a + 9)2
B. (a - 8) (a + 8)
C. (a + 9) (a -9)
D. (a – 7)(a +7)
A. (a + 9)2
B. (a - 8) (a + 8)
C. (a + 9) (a -9)
D. (a – 7)(a +7)
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4. a² - 81
Use the sum-product pattern
a² - 81
a² + 9a - 81
Common factor from the two pairs
a² + 9a - 9a - 81
a(a + 9) - 9 (a + 9)
Rewrite in factored form
a(a + 9) - 9 (a + 9)
(a - 9)(a + 9)
Solution:
(a - 9)(a + 9)